George Gough, a Sacramento lobbyist for Monsanto, a leader in developing FDA-approved bioengineered crops, said the industry relied on federal guidelines and didn't believe states should have a role in labeling.

"Just because it's biotech doesn't mean it has to have a label," Gough said.

The FDA's policy is that transgenic crops are "substantially equivalent" to traditional crops and don't need labeling if they don't modify the nutritional value, composition or capacity to cause allergic reactions.